The objectives of this research are a. to analyze the control mechanisms that govern the assignment of positional information to cells in regulating and transdetermining imaginal discs of Drosophila melanogaster, and b. to search for region-specific differences in the patterns of protein synthesis within imaginal discs. In a first group of experiments we will determine the detail sequence with which new pattern elements appear in imaginal discs undergoing terminal regeneration or transdetermination. Leg and antenna imaginal discs deprived of their distal regions will be allowed to proliferate for different lengths of time prior to metamorphosis. We will analyze whether a specific set of positional values provides transdetermination-competence to the cells that carry them, by testing cells which have regenerated these values for their ability to transdetermine. A clonal analysis of cells from the transdetermination-competent region in the leg disc will be performed in order to re-evaluate the question about the requirements necessary for transdetermination. In a second group of experiments the protein-synthetic patterns of cells from different regions along the proximo-distal axes of leg and wing imaginal discs will be studied, by separating radioactively labelled proteins on two-dimensional polyacrylamide gels by electrophoresis. Of special importance is the question whether homologous regions in the two discs have protein species in common that are lacking in other disc regions. Such proteins might be involved in the specification and cell-to-cell communication of positional information in imaginal discs.